Exercise equipment, such as weight lifting equipment is popular across all strata of society, including amateurs and professional athletes alike. Users of such equipment include anyone wishing to improve strength physique, or overall muscle conditioning. In practice, weight training uses the weight force of weighted bars, weight stacks or the to oppose the force generated by muscle. Weight training typically includes the use of specialized equipment to target specialized muscle groups. Such equipment may include free weights, such as dumb bells, bar bells, and kettle bells, or such equipment may include weight machines. There is a fairly large number of weight machines manufactured today. For example, one type of machine includes a barbell that is partially constrained to move only in a vertical manner. Cable-type machines may include two weight stacks with cables running through adjustable pulleys to handles. There are also exercise specific weight machines that are designed to target specific muscle groups or multi-use machines that include multiple exercise-specific capabilities in one apparatus. Another variety includes the use of cam mechanisms (such as those made by Nautilus®) that enable the user to maintain constant or variable muscle force throughout the exercise movement.
Common weight machines may include the use of rectangular weight plates, commonly referred to as a weight stack. In use, the stack may include a hole designed to accept a vertical support bar having a series of holes drilled therein to accept a pin. Each of the plates in the stack may further include a channel or a hole through the middle that aligns with one of the holes in the support bar. When the pin is inserted through the channel or hole, into a selected hole on the bar, all of the plates above the pin rest upon it, and are lifted when the bar rises. The plates below do not rise. Machines of this type provide various levels of resistance over the same range of motion depending on the number of plates resting on the pin to be lifted.
Machines which use a weight stack may vary according to the manner in which the bar is raised. For example, some machines may include a roller and lever combination, while others may include a hinge and lever combination. Still others may include the use of cables, belts or similar devices attached to the bar, with the cable or belts running over a wheel or pulley.
Many manufacturers are known to design and manufacture weight machines. Such manufacturers include Vectra®, FreeMotion™, and MedX®, among others. Manufacturers have each developed systems and machines for aiding the user in developing the desired results. Common weight machines include the use of cables, free weights and levers.
An example of a manufacturer that uses lever-type technology in its equipment is MedX®. As mentioned, the weight stack typically includes a hole designed to accept a vertical support bar having a series of holes drilled therein to accept a pin. As the stack is raised and lowered during use, the stack rides on the vertical support bar, creating friction.